1. Field of the Invention
The present invention relates to a nozzle plate, a method of manufacturing a nozzle plate, a liquid ejection head and an image forming apparatus, and more particularly, to a nozzle plate provided in an inkjet type of liquid ejection head which ejects a liquid droplet (ink droplet) from a nozzle (a nozzle hole).
2. Description of the Related Art
In general, the recording head of an inkjet recording apparatus (inkjet head) comprises a nozzle forming substrate (nozzle plate) in which a plurality of nozzle holes are formed, and it performs recording on a recording medium by pressurizing the ink inside pressure chambers, through the use of energy generating devices such as piezoelectric elements or heat-generating elements, for example, thereby causing ink droplets to be ejected respectively from the nozzles connected to the pressure chambers.
To form such a nozzle plate, for example, a resist pattern corresponding to the nozzle holes is formed on a conductive substrate, and an overhang electroforming process is then carried out to precipitate a metal material such as nickel onto the conductive substrate so as to cover a portion of the resist pattern, whereby trumpet-shaped (curved) nozzle holes which converge in diameter toward the ink ejection side are formed in the substrate. By adopting a nozzle hole shape of this kind, it is possible to restrict loss of the ejection energy applied by the energy generating device, and therefore it is possible to improve the ejection efficiency of the inkjet head.
Furthermore, it is known that in an inkjet head, the shape, accuracy, and the like, of the nozzle holes affect the ink droplet ejection characteristics, and furthermore, that the surface characteristics of the nozzle plate also affect the ink droplet ejection characteristics. For example, if ink adheres to the nozzle perimeter regions on the surface of the nozzle plate, then problems may arise in that the ejection direction of the ink droplets is deflected, variation occurs in the size of the ink droplets, the ejection speed of the ink droplets becomes instable, and so on. In order to prevent these problems, in general, a lyophobic film (liquid-repellent film) is formed on the surface (ink ejection surface) of the nozzle plate, with the purpose of stabilizing the ink droplet ejection characteristics.
Japanese Patent Application Publication No. 2001-38913 teaches a method in which, in order to form a lyophobic film on the surface of the nozzle plate, a lyophobic film is formed after masking the interiors of the nozzle holes with resist. However, according to this method, the meniscus comes to vibrate on the side adjacent to the surface of the nozzle plate, the ink wets and spreads onto the surface of the nozzle plate, and therefore the ink droplet ejection characteristics become instable.
On the other hand, Japanese Patent Application Publication No. 2001-187453 discloses a nozzle plate in which, in order to achieve stable ejection of ink droplets, a portion of a lyophobic layer (ink-repelling film layer) which covers the surface of the nozzle plate is made to enter into and extend over the inner surfaces of the nozzle holes.
However, in the nozzle plate described in Japanese Patent Application Publication No. 2001-187453, the amount by which the lyophobic layer extends over the inner surfaces of the nozzle holes is governed by a photosensitive resin film which is introduced inside the nozzles by heating and pressurization, and taking account of the temperature distribution, pressure distribution, and the like, it is difficult to achieve a uniform amount of extension of the lyophobic layer into the nozzles, over the whole of the plate.
Furthermore, in the nozzle plate described in Japanese Patent Application Publication No. 2001-187453, the lyophobic layer is formed by eutectoid plating of a fluorine polymer material, but there is a possibility that step differences are created in the eutectic plating layer on the inner surfaces of the nozzle holes and hence smooth ink flow is inhibited.